1. Field of the Invention:
This invention relates to an heat insulating engine consisting mainly of a ceramic material and provided with an auxiliary combustion chamber.
2. Description of the Prior Art:
A conventional heat insulating engine utilizing a ceramic material as a heat resisting material is disclosed in, for example, Japanese Patent Laid-Open No. 46317/1984. The parts of a combustion chamber in the internal combustion engine will now be described with reference to FIG. 2. The parts of the combustion chamber in the internal combustion engine include parts constituting an auxiliary combustion chamber, a cylinder head 41, a cylinder liner 44, a piston 45, and parts of a combustion chamber which constitute the inner surface of the combustion chamber, and these parts are formed out of a ceramic material having excellent heat insulating characteristics. The cylinder head 41 is combined with a cylinder block 42 via a gasket 43, and the cylinder liner 44 is fixed to the cylinder block 42. A vortex chamber 47 formed in the cylinder head 41 consists of upper and lower vortex chamber members 48, 49 fitted in the cylinder head 41. The lower vortex chamber 49 is provided with an ejection port 50 which communicates the vortex chamber 47 and a main combustion chamber 46 with each other. A fuel injection nozzle 52 and a glow plug 53 are provided in the cylinder head 41. The upper and lower vortex chamber members 48, 49 are formed as combustion chamber parts out of a ceramic material of a non-oxide of silicon, such as a silicon nitride ceramic material and a silicon carbide ceramic material. The material of the surfaces defining the vortex chamber 47 and ejection port 50 is converted into a silicon oxide ceramic material due to the heating of the non-oxide ceramic material to a high temperature. A thin layer of a catalyst of a noble metal, such as platinum, rhodium and palladium is formed on each of these surfaces by spattering. Owing to such a construction, these combustion chamber parts prevent the separation of a thin layer 51 of a noble metal catalyst, minimizes the deterioration of the catalyst and reduces an unburnt hydrocarbon content of an exhaust gas.
However, it is very difficult to sufficiently obtain the heat insulating characteristics in a heat insulating engine having a cylinder head utilizing these ceramic materials as heat insulating or heat resisting materials, and, in such an engine, the wall thickness is increased for the purpose of meeting the requirements. Namely, the portions of such an engine which face the combustion chamber can be formed so that they can withstand a high-temperature combustion gas, by making them of a ceramic material, such as silicon nitride having high thermal resistance and thermal shock resistance and excellent heat insulating characteristics. However, when the wall thickness is too large, the thermal capacity of the wall surface increases. Consequently, the suction air receives the heat energy accumulated on the inner surface, and is thermally expanded, so that the suction efficiency decreases.
The thicknesses of the constituted parts of the combustion chamber in the internal combustion engine disclosed in Japanese Patent Laid-Open No. 46317/1984 referred to previously are all large, and the thin layer 51 consists of a noble metal as mentioned above. In addition, the upper and lower vortex chambers 48, 49 are formed out of a ceramic material of silicon nitride or silicon carbide which has a high heat resistance and not so good heat insulating characteristics. Therefore, the thermal capacity of the surface of each part of the combustion chamber becomes high, and the thermal capacity of the parts exposed to a high temperature cannot be reduced to a low level. This makes it impossible to prevent a decrease of the suction efficiency. Moreover, it is impossible in this construction to speedily carry out the mixing of atomized fuel with air.